This invention relates to an absolute linear position detection device used for a positioning device or the like and, particularly, to a position detection device realizing an enlarged detection range within which a position can be detected in an absolute value with a simplified construction.
Japanese Preliminary Utility Model Publication No. 136718/1983 filed by the applicant of the present application discloses a detection device in which a magnetic substance portion and a non-magnetic substance portion are alternately and repeatedly provided on a rod section in the logitudinal direction thereof, a magnetic type detection head (detection sensor) comprising a primary coil and a secondary coil is provided in proximity to this rod section, the rod section is relatively displaced with respect to the sensor in accordance with mechanical linear displacement which is the object of detection, and an output signal corresponding to absolute position of the rod section relative to the sensor is derived from the sensor. This prior art device, however, has the problem that the range within which the position can be detected in an absolute value is limited to the length of one pitch of repetition of the magnetic substance portion and the non-magnetic portion.
U.S. Pat. No. 4,572,951 (Particularly FIG. 9) discloses a device in which a plurality of rod sections are provided, the pitch of repetition of a magnetic substance portion and a non-magnetic portion is made different from one rod section to another and detection of position over a wide range is realized by processing absolute position detection data concerning respective rod sections.
Although U.S. Pat. No. 4,572,951 can expand the range of detecting an absolute position, it has the problem that it necessitates a complex construction for it requires a plurality of rod sections.